1. Field of the Invention
The present invention is broadly concerned with the promoter of the ribosomal protein gene L25. More particularly, the present invention relates to an isolated DNA molecule and an expression vector, each of which comprises the promoter of the ribosomal protein gene L25; a plant cell and a plant, each of which is transformed with this expression vector; a seed obtained from this plant; and a method for producing a product from this plant or plant cell.
2. Description of the Related Art
As components of ribosomes, ribosomal proteins (r-proteins) are critical in protein biosynthesis required for cell division and cell differentiation. Studying the expression of ribosomal protein genes and their regulation enables one to differentiate the functions of important housekeeping genes in plant growth and development. Moreover, some promoters of ribosomal protein genes, due to their high expression and complex regulation patterns, are among the most suitable candidates for expressing exogenous genes that are of economic or medical importance.
Different plant ribosomal protein genes appear to have different expression patterns that are regulated in a complicated fashion, a conclusion drawn from studying at least 12 small (5) ribosomal genes and 13 large (L) ribosomal genes from a variety of tissues in several plants (Lee et al. 1999. Gene 226:155-163). Among these 25 ribosome protein genes, L3 and L16 in Arabidopsis (Kim et al. 1990. Gene 93:177-182; Williams et al. 1995. Plant J. 8:65-76) and S15a in rapeseed (Bonham-Smith et al. 1992. Plant Mol. Biol. 18:909-919) were highly expressed in all rapidly proliferating organs, including shoot and root apical meristems, lateral root primordial and early developing stages of reproductive organs. This pattern of ribosomal protein gene expression is consistent with that of most ribosomal protein genes in prokaryotes (Mager 1988. Biochim Biophys. Acta 949:1-15). The rpL16 in Arabidopisis is encoded by two genes (rpLA and rpL16B), and both are mainly regulated in the level of transcription (Williams et al. 1995. Plant J. 8:65-76), ribosomal protein genes in prokaryotes (Mager 1988. Biochim Biophys. Acta 949:1-15). The rpL16 in Arabidopisis is encoded by two genes (rpLA and rpL16B), and both are mainly regulated in the level of transcription (Williams et al. 1995. Plant J. 8:65-76), similar to the plastid ribosomal protein L21 (RPL21) in spinach (Lagrange et al. 1997. Plant Cell 9:1469-1479). While RPL 16A was mainly found in proliferating tissues including the shoot and root apical meristems and auxin-induced lateral root primordia, RPL 16B was highly expressed in cells in the root stele, anthers, and auxin-induced lateral root primordia.
The expression of S19 and L7 in potato increased at the transcription level in the stolon tip during the early stages of tuberization but maintained at a low level in leaves, stems, and roots throughout the development (Taylor et al. 1992. Plant Physiol. 100:1171-1176). Genes S11and S13 in maize were expressed at higher transcriptional level in roots and shoots of developing seedlings than in fully expanded leaf tissues (Lebrun et al. 1991. Plant Mol. Biol. 17:265-268; Joanin et al. 1993. Plant Mol. Biol. 21:701-704). The levels of L27 mRNA in pea were increased remarkably by decapitation, a treatment that leads to cell proliferation (Stafstrom et al. 1992. Plant Physiol. 100:1494-1502; Stafstrom et al. 1995. Plant Mol. Biol. 29:255-265). The transcript of S16 in rice was essentially the same across different tissues and development stages (Zhao et al. 1995. Plant Physiol. 107:1471-1472)
The further understanding of the mechanism of how genes are regulated at transcription level can be greatly enhanced by identifying cis-acting elements, their binding protein(s) and their interaction. By transient and stable transfection analysis of RPL21 promoter deletion mutants, Lagrange et al. (1997) identified a strong core promoter sufficient to drive high levels of gene expression and two non-overlapping positive and negative domains that modulate core promoter activity independently of light. Further, gel retardation analysis showed that a cis-acting element located in the positive domain (S2) binds a leaf-specific nuclear factor (S2F). The rpL34 promoter region recently has been characterized and two synergically functional, yet separable cis-acting elements, have been defined (Shi et al. 1999. Amer. Soc. Plant Physiol. Annual Meeting, Baltimore, Md.).
In a previous study, one cDNA encoding tobacco ribosomal protein L25 (rpL25), which RNA is most abundant in three-day-old cell suspension culture and post germinating seedlings, was isolated and partially characterized. L25 mRNA levels increased in response to wounding and plant hormone treatment (Gao et al. 1993. American Chemical Society Symposium in Denver), a pattern similar to the expression of L27 gene. In this investigation, rpL25 genomic DNA clones were isolated and partially characterized. A preliminary functional analysis of the promoter was performed to gain insights of the expression of rpL25 gene.
The present invention is directed to an isolated DNA molecule comprising the promoter of the ribosomal protein gene L25, wherein the promoter is preferably the promoter of Nicotiana tabacum, and the promoter ideally comprises the nucleotide sequence shown in FIG. 3.
The invention also concerns an expression vector comprising the promoter of the ribosomal protein gene L25 and a structural gene operably linked thereto, wherein the promoter is preferably the promoter of Nicotiana tabacum, and the promoter ideally comprises the nucleotide sequence shown in FIG. 3.
Additionally, the invention relates to a plant cell or whole plant transformed with one of the above-described expression vectors, and to seed obtained from one of these plants.
Finally, the invention is directed to a method for producing a product, e.g., a protein, from one of the above-described plants or plant cells, comprising providing the plant or plant cell, causing a product encoded by the structural gene to be produced in the plant or plant cell, and isolating the product from the plant or plant cell, thereby producing the product.